1. Field of the Invention
The present invention relates to a wind turbine generator, more particularly, to a cable holding structure for holding a cable suspended from the nacelle of the wind turbine generator.
2. Description of the Related Art
One distinctive feature of a wind turbine generator is that main components constituting the wind turbine generator, such as a generator, a pitch control system and a yaw control system, are provided away from the ground. More specifically, a nacelle is provided on the top of a tower so that the nacelle is rotatable in the azimuth direction, and the nacelle is installed with a generator, the gear box, a pitch control system and a yaw control system.
Cables are suspended inside the tower to connect the components installed in the nacelle to facilities provided on the ground (such as in-site transmission lines and a SCADA (Supervisory Control And Data Acquisition)). The suspended cables include a power cable connected to the generator, and a control cable used for controlling the components installed in the nacelle. It is important in increasing the reliability of the wind turbine generator to appropriately design a cable holding structure which suspends and holds these cables.
One difficulty of the cable holding structure is how to deal with the rotation of the nacelle. Since a twist is given to the cable by the rotation of the nacelle, it is desirable that the cable holding structure is so designed as to structurally absorb the twist of the cable. U.S. Pat. No. 6,713,891 B2 discloses a cable holding structure that gives a downwards curve to a cable by using a fixing device provided with an upward curved plate so that the twist of the cable is absorbed by this downwards curve. Further, U.S. Pat. No. 6,713,891 B2 also discloses a cable holding structure for maintaining adjacent cables to be spaced at a constant distance.
Another difficulty of the cable holding structure is that, when the wind turbine generator is driven, the tower is largely shaken and hence the cables are largely swung. When the cables are largely swung, it may cause a contact between a structural member (e.g., a ladder) in the tower and the cables, resulting in damages of the cables. U.S. Patent Publication No. 2009/0206610 (A1) discloses a wind turbine generator provided with a first cable guard for covering a ladder and a second cable guard of a tubular shape for suppressing a movement of a cable in a tower.
However, there is room for improvement in these known cable holding structures in view of avoiding the cables being damaged.